Four lens photographic objective



SEARCH RUOM June 17, 1958 JIRO MUKAl FOUR LENS PHOTOGRAPHIC OBJECTIVEFiled May 25, 1956 FIG.

IN V EN TOR. d/Ro MuKA/ United States Patent FOUR LENS PHOTOGRAPHICOBJECTIVE Jiro Mukai, Mnsashino City, Tokyo, Japan, assignor to CanonCamera Company, Inc., Otaku, Tokyo, Japan, a corporation of JapanApplication May 23, 1956, Serial No. 586,691

Claims priority, application Japan November 12, 1955 1 Claim. or. 88-57)This invention relates to a four lens photographic objective and moreparticularly to an improvement in triplet arrays comprising four lenses.

An object of this invention is to minimize various aberrations such aschromatic, spherical, distortional and others as compared toconventional lenses, and more particularly to correct coma, astigmatismand distortion most efiectively.

A clear concept of the scope and purpose of this invention may beobtained from the following description, taken in connection with theattached drawing, in which:

Fig. 1 is a sectional view of an illustrative embodiment of theobjective according to this invention, the objective having an angle offield 46 and an aperture of'F:2.8;

Fig. 2 shows the curves for the spherical aberration and the deviationfrom the sine condition, in which graph S represents the sphericalaberration for the d-line of the spectrum, S,;' the deviation of thed-linc of the spectrum from the sine condition, S the sphericalaberration of the spectrum g-line, and S the deviation of the g-linefrom the sine condition;

Fig. 3 shows the graph of the astigmatism, graph A representing thesagital field curvature and A the meridional field curvature; and

Fig. 4 shows the distortion graph D for each angle of incidence. I

This invention proposes an improved construction of and the thirdcomponent consists of a negative lens L and a positive lens L, with theconvex surface of their intercemented surfaces facing towards theobject.

The triplet objective of the instant invention is constructed accordingto the following requirements:

(1) The difference between the refractive indices for the d-line of thespectrum of the cemented lens elements L and L, of the third component(n -n lies between 0.166 and 0.2;

(2) The thickness d on the optical axis of the last positive lens memberL lies between 0.1 f and 0.15 wherein f is equivalent focal length ofthe objective;

(3) Air space d between the first component L and the second component Llies between 0.045 f and 0.075

(4) The average value of the refractive indices for the d-line of thespectrum of the positive lens members L and L that is,

lies between 1.65 and 1.75;

() The average value of the refractive indices for the 2,838,978Patented June 17, 1958 lies between 1.5 and 1.6;

(6) The ratio of the radii of curvature of the second surface r: and thefirst surface r of the first component L lies between 18 and co;

(7) The radius of curvature of the front surface r, of

the second component L lies between 0.6 f and 0.84

. represent the radii of curvature of.

wherein r r the successive optical surfaces counting from the front ofthe objective; (1,, d represent the axial thicknesses and the air spacesof each element; n n represent the refractive index for d-line of thespectrum of each element L L and v v represent Abbes dispersive indexthereof. Generally speaking, giving the difference in the refractiveindices for the d-line of the spectrum of the cemented lens elements Land L, of the third component as large a value as possible serves todecrease coma, however, the meridional image plane is curvedconsiderably towards the side of objective.

in this invention, however, by imposing the above mentioned condition(1) that 0.2 (rm-11 0.166, the coma is corrected and the curve of themeridional image plane is rectified by conditions (2) and (3) that 0.1 fd 0.15 f and 0.045 f d 0.075 f mentioned above. Also by the abovementioned conditions (4) and the Petzval sum is minimized and a flatimage plane is obtained by limiting in the above mentioned conditions(6) and (7) that Thus it is quite obvious that chromatic, spherical,distortional and other aberrations as mentioned above can be minimizedas compared with the conventional lenses and more particularly a highgrade triplet lens is obtainable that remarkably corrects the comatic,astigmatic and distortional aberrations.

An example of the embodiments according to this invention is givenbelow:

What I claim is: I

A photographic objective corrected for spherical and chromaticaberration, coma," astigmatism, field curvature and distortion,comprising a single element front component L in the form of acollective meniscus with its convex surface having the curvature 1',toward the object side of the objective, at second single elementcomponent L is a dispersive biconcave element air spaced from the firstcomponent with its stronger concave surface of curvature n, towards theimage side, and a third component spaced from the second componentcomprises a dispersive element L cemented to a collective element L thecemented surface of the convex curvature r facing the object side,wherein the radii of curvature rsubsmpt of the Lenses Radil ThicknessRefractive Abbe spacings Index Number r ==0.379 L1 d|=0.097 m=1.6583v1=57.3

d:=0.072 T3=0.741 L1 d;=0.027 m=1.5930 Uz=34.3

d4=0.061 f5=b L; d =0.021 m=1.5111 v3=60.6

ru=0.348 L4 d =0.136 m=1.6910 v4=54.8

References Cited in the file of this patent UNITED STATES PATENTS

